"When you sign up for 2-Step Verification, we normally send you verification codes. However, these codes do not work with some apps and devices, like Gmail on your iPhone or iPad, Thunderbird, and Outlook. Instead, you'll need to authorize the app or device the first time you use it to sign in to your Google Account by generating and entering an App password," explains Google.

Here's an example of password generated by Google (it always has 16 characters, but you'll only have to enter once, so don't worry about memorizing it):